Good clover-ryegrass mix vital for a productive pasture

Good clover-ryegrass mix vital for a productive pasture

The importance of having a good mix of clover and ryegrass to produce better feed quality and yield has been somewhat forgotten and most farms don’t grow enough clover.

With more emphasis on a ‘pasture first’ approach for restoring profitable margins on farms, clover’s vital role has taken on renewed significance. DairyNZ principal scientist, feed and farm systems, David Chapman, DairyNZ scientist, Laura Rossi and Doug Edmeades of AgKnowledge Ltd, explain the core elements of productive pastures.

Key points

The core elements of productive pastures are best met by mixtures of ryegrass and white clover.

When clover comprises between 10 and 40 percent of total dry matter (DM) in summer, there are gains in DM of between 1.4 and 3.4 t DM/ha per year.

Excessive focus on nitrogen (N) fertiliser and failure to meet the soil nutrient requirements of white clover in recent years have inhibited clover growth and compromised pasture productivity.

Putting pasture first for profitability

The recent re-focus on using pasture first, and using it efficiently for animal feeding is critical for restoring profitability margins in the industry. ‘Pasture First’ is essentially matching feed demand to feed supply to maximise pasture eaten. The best results are achieved when this is implemented on a productive pasture base and supported by good decision-making based on monitoring information. The first step is calculating current pasture eaten on your farm and comparing this with other farms in your region. You will then know the pasture growing potential in your area, and whether there is a ‘gap’ between potential and your current estimate for your farm.

Closing the gap: What makes up a ‘good’ pasture?

A ‘good’ pasture is one that meets the nutritional requirements of cows over as much of the annual cycle as possible, year-on-year. To achieve this, there are four primary requirements:

Growth rates are close to the potential set by the climate and soils of the farm. Both the total amount of pasture grown for the year, and the time of year when the pasture produces feed, are important.

The feed produced is of adequate nutritional value for cows to perform to expected levels. The key factor here is the metabolisable energy (ME) density of the feed, which is mainly governed by the pasture’s green leaf content.

Animals can sustain high rates of intake from pasture, so that they can achieve high production without compromising ability to graze pastures back to target residuals. This also relates to the bulk density of green leaf available in the pre-graze pasture.

The pasture enables the farm system to meet limits required by regional environmental plans (e.g. for freshwater quality). Ideally, pastures should require low to moderate inputs of N fertiliser to reach maximum yield, and/or not accumulate excess N in herbage so that animals are not eating and excreting large surpluses of N1.Growth rate is controlled mainly by environment, but also by management. Points 2 and 3 are mainly about management. If these primary requirements are met, then it is likely that one further, secondary, requirement will also be met:

The pasture contains a high proportion of the sown species and a low content of weeds that restrict the biological efficiency of the pasture. An abundance of weeds is generally a signal of terminal pasture decline.

Herbage samples can be analysed for ME and other nutritional components.

Soil tests tell us if there is enough of the right nutrients available for the sown species to out-compete the weeds.

The Pasture Condition Score tool3 is a simple method for visually assessing weed species content and ground cover of the sown species as a guide toward pasture renewal.

Although there is a plethora of tools available, anecdotal feedback from farmers has highlighted a growing concern that pasture management skills in the industry are in decline. It’s important to re-visit and re-activate the toolbox with your farm team.

Past issues of DairyNZ’s Technical Series have covered the principles and practices for maximising pasture growth rate through grazing management4,5,6 and nutritional value of well-managed pasture as a complete diet for dairy cows7. Refer to these for further information.

White clover: the forgotten component of high-producing pastures?

For the vast majority of NZ dairy farms, the list of requirements on the previous page describes a pasture with a high content of perennial ryegrass and white clover. The contribution of white clover to N supply (from biological fixation) and pasture nutritional quality in grass/clover mixtures is beyond dispute. Despite the benefits, clover typically contributes less than 15 percent of total annual DM in NZ dairy pastures8, well below the 30 percent contribution considered necessary to capture the animal productivity benefits9.

Less well recognised are the yield benefits available when clover contributes 20-30 percent of total annual DM, even though these too have been known for many years10. Increased use of N fertiliser in the pursuit of higher milk production over the past two decades has suppressed clover performance, since the negative impact of N fertiliser rates on clover percentage in mixed pastures is also beyond dispute.

Recent experiments exploring grass/clover interactions in dairy pastures11 have bought the yield advantages of mixed pastures with moderate-high clover percentage in the total DM back into the limelight. In three studies, one in Waikato and two in Canterbury, seasonal and total annual yields were measured for pastures sown either with or without clover (+ clover and – clover respectively), and receiving either low rates of N fertiliser (50 and 100kg/ha/year in Waikato and Canterbury respectively) or high rates of N (225 and 325kg/ha/year in Waikato and Canterbury).

In all, seven years of total annual DM yield data are available. Yields were significantly greater in the + clover treatment than the – clover treatment in all years. The yield advantage to + clover was greater at low N levels (3.4 t DM/ha, +42 percent) than at high N levels (1.4 t DM/ha, +12 percent). This was expected because competition from grass was restricted due to lower N inputs. Across all of these experiments, mean annual white clover content decreased one percent for every additional:

13kg N/ha above 100kg N/ha/year in Canterbury, and

19kg N/ha above 50kg N/ha/year in Waikato.

The yield increases described above are valuable, since almost all of the additional feed comes in summer (Figure 1) when it is has high economic value12 and it is of high digestibility, due to the clover content.

White clover: how can farmers get more of it?

The answer to this question hinges around managing competition between grass and clover. While the ryegrass/white clover pasture is an ‘ideal’ mixture, the reality is that ryegrass and clover plants are in constant competition with each other for light, water and nutrients.

When we review what is known about the competitive ability of ryegrass and white clover, the score card looks something like this:

Competition for light: Winner = ryegrass, Loser = clover

Competition for water: About even (perhaps a slight edge to ryegrass)

Competition for nitrogen: Winner = clover (it fixes its own N) but N fertiliser negates this

Competition for nutrient: Winner = ryegrass, Loser = clover

Therefore, ‘home-ground’ advantage for white clover is on soils that are low in N but high in phosphorus (P), potassium (K), sulphur (S), and, sometimes, magnesium (Mg) and molybdenum (Mo). Nitrogen is the only resource where clover is the clear winner, but, this advantage can be negated by high N fertiliser inputs. Total annual fertiliser inputs of less than 200kg N/ha combined with excellent control of pre-and post-grazing pasture cover to limit the shading competition from ryegrass is essential if clover content in the range 20-40 percent of total DM is to be achieved9.

However, recent excessive focus on nitrogen and failure to recognise that white clover needs different amounts of the other major nutrients compared with ryegrass, has contributed to sub-optimal clover content and reduced pasture productivity on New Zealand dairy farms. Fortunately, the information required to rectify these issues is already available – it, like the required nutrients, just needs to be applied.

White clover: nutrient requirements

White clover requires 16 nutrients and can only grow as fast as the most limiting nutrient2. Furthermore, white clover has a poor root structure relative to grasses. As a consequence, higher concentrations of nutrients in the soil are required to optimise its production relative to grasses. It is for this reason that white clover can be regarded as the canary in the mine. If all 16 nutrients are not present in the soil at the optimal levels then white clover will not thrive.

The optimal soil nutrients levels for white clover-based pasture are given in DairyNZ Farm Fact 7-52, together with the critical nutrient levels for clover herbage. If these levels are not achieved then the clover will not compete against the ryegrass and the clover content in the pasture will decline. When this happens, less clover N is fixed and returned to the soil and hence the ryegrass component will also decline, unless of course fertiliser N is applied.

There are some obvious visual symptoms in clover-based pastures if the soil fertility is less than optimal. In the absence of fertiliser N the excreta patches will become prominent and very little clover will be found in the non-excreta patches which will also contain a high weed loading, particularly flat weeds.

A good soil fertility monitoring plan including soil tests and clover-only samples is essential to managing the fertiliser inputs for optimal pasture production2.